Amass of 8 kg. moves at a rate of 14.3m/ sec. what is the ke developed by the mass

       Kinetic energy = (1/2) (mass) (speed)²

                             = (1/2) (8 kg) (14.3 m/s)²

                             =    (4 kg)  (204.49 m²/s²)

                             =        817.96 joules .

The mass doesn't 'develop' that energy.  That's the energy it has
when it's moving 14.3 m/s, and you have to give it that energy in
order to make it move at that speed.  The energy has to come from
someplace, and if you can't deliver it to the mass, then there's no way
to make the mass move at 14.3 m/s.

The answer is trial 3.